Such a diagnostic device and diagnostic method is known from the patent publication U.S. Pat. No. 5,680,109. The device is connected to two impulse lines, which are coupled to a process fluid of a process, and either senses the two absolute pressures in the two impulse lines or one absolute pressure in one impulse line and one differential pressure between the two impulse lines. The device processes the pressure signals so as to extract from them vibration noise signals carried in the process medium (e.g., liquid, gas). Such vibration-related processed signals are then evaluated, with the evaluation ending in an output indicating that the impulse lines are not blocked or that at least one of the impulse lines are blocked.